The present invention relates to a method and apparatus for location of faults in a mobile radio telecommunications system as well as a base station and a network element specially adapted for assisting in the location of faults as well, as a method of operating the base station and the network element.
FIG. 1 is a schematic representation of possible organizations of base station transceivers S, M, MS with respect to a base station controller (BSC) 6 in a cellular radio mobile telephone system. Typically, each base station S 1-3, M 1-4, SM 1-9 is connected to the BSC 6 by means of a data telecommunications link 1-5, e.g. a Pulse Code Modulated (PCM) link. There are various ways of arranging the PCM links. One simple way is to connect each base station transceiver S 1-3 by means of a single communications link, e.g. a cable or microwave link 2, directly to the BSC 6 to form a star configuration. Alternative methods include multidrop connections to base station transceivers, e.g. a single multidrop with a linear series of base station transceivers M 1-3 connected together by a communications link 4, or a multidrop configuration in the form a ring of transceivers SM 1-9 connected by a communications link 5 which allows the feed to be either anticlockwise or clockwise.
One problem which is particularly marked with the star configuration is the location of faults. A more detailed drawing of such a known base station transceiver (BTS, 10) is shown in FIG. 2. BTS 10 is similar in architecture to S2000, S4000 or S8000 indoor or outdoor BTS as supplied by Nortel Networks, Guyancourt, France. The BTS 10 includes a base common function unit (BCF) 11, a transmitter receiver unit (TRX) 12 and a power supply unit (PSU) 13. The BCF unit 11 includes a control and switch double board (CSW1 and CSW2) 15, 16 to manage the BTS 10, to configure and supervise the other modules in the BTS 10 as well as to control the BTS operations and maintenance requirements. The BCF 11 also includes an alarm circuit 26 and a signaling concentrator 19. The BCF 11 also provides through the synchronization unit 18 the necessary timing for all the modules in the BTS 10, e.g. the reference clock for TDM radio signals on the air interface 22. The BCF 11 also provides conversion of external signals from the BSC to internal signals and vice versa. The PCM interface (DTI) 17 provides control of the incoming signals from, and the outgoing signals to the BSC usually in the form of pulse code modulated (PCM) signaling. The BCF 11 also provides the necessary switching of the PCM slots, in particular, the multiplexing and demultiplexing of the signaling channels between the TRX 12 and the PCM slots.
The TRX 12 provides full duplex operation on the radio interface 22, e.g. transmission of signals via the transmitter 25 and transmission coupler 27, amplification of the received radio frequency signals from the air interface 22 via the transmission coupler 27 and receiver 24 and TDMA frame processing in the frame processing unit 23. Transmission coupler 27 may be a duplexer. Further, TRX 52 may include a second antenna for spatial diversity, the main antenna 28 and the second antenna 29 being connected to the receiver RX 64 via a splitter 21. Usually, there are several TRX 25 in any transceiver, first of all to provide redundancy and secondly so that at least one TRX may broadcast the beacon or pilot signal which is used by mobile units to locate the cell and to identify the BTS and make contact with it.
Fault situations are summarized in table 1. A fault in the PCM link means that the BTS 10 may be functioning correctly but there is a problem in the cable link from the BSC 6 to the BTS 10. A major fault in the BTS means that the BTS 10 is not able to set up a PCM link to the BSC 6 despite the fact that the PCM communication link is working correctly. A fault in the TRX means that the transmitter is faulty but this can be alleviated by transfer of the functionality of the affected TRX to another TRX.
For the state F2 a fault occurs in one of the TRX 25. This results in the operation of this TRX being taken over by another TRX in the BTS 10 so there is no loss of the beacon signal and no loss of user calls provided the capacity is not exceeded. In states F1 and F3 the PCM signal and information derived therefrom (e.g. timing) is not provided within the BCF 11. This may result in no beacon signal being propagated and service being lost. The operation and maintenance system (which may be operated by a different entity than the network provider) cannot distinguish between a fault in the DTI 17 and a fault in the PCM connection to the DTI 17 because it is not provided with sufficient information from the network elements such as the BTS 10 and/or the BSC 6.
Accordingly, when such a fault occurs a crew may be dispatched to test and rectify the fault. This involves going to the BTS 10 in question and determining whether the PCM interfaces 17, the BCF 11, and the TRX""s are working properly are working correctly and that therefore the fault lies in the PCM connection. This wastes time and is an expensive solution.
GB 2,287,157 describes an operations and maintenance system for a base station transceiver which is connected to a base station controller to provide remote monitoring of the base station transceiver. The remote monitoring uses the PCM link to the base station transceiver so that loss of the PCM link for some reason means simultaneous loss of the remote monitoring facility.
It is an object of the present invention to provide a mobile radio communications system and a method of operating the same which can be reliably identify faults in a communication link to a base station transceiver without requiring an on-site inspection.
The present invention includes a mobile telecommunications system comprising network having at least one base station transceiver for communication with mobile terminals within a first geographic area; the network being adapted for communicating messages to an from the at least one base station transceiver; the at least one base station transceiver being connected to a first communications link of the network for receipt and transmission of user messages; the at least one base station transceiver being adapted so that when the at least one base station transceiver detects a fault in the first communications link the at least one base station transceiver continues to transmit a beacon or pilot signal; and the network is adapted to monitor activity of the mobile terminals for determination of whether the beacon or pilot signal is being transmitted from the at least one base station transceiver. A resource manager may carry out the monitoring of mobile terminal behavior. The resource manager may be located in a network element such as a base station controller. The mobile terminal activity to be monitored may be attempts by mobile terminals to handover to the at least one base station transceiver or to perform a forward handover from the at least one base station transceiver to another base station transceiver in the system or to perform a call re-establishment with another base station transceiver, or signal strength measurements of beacon signals from the at least one base station transceiver reported by mobile terminals communicating with a base station transceiver other than the at least one base station transceiver. In a CDMA system the mobile terminal activity may be requests for the at least one base station transceiver to be placed on the Active list as this is an indication that the pilot signal is being received.
The present invention also includes a method of operating a mobile telecommunications system having at least one base station transceiver for communication with mobile terminals within a first geographic area, the at least one base station transceiver being connected to a first communications link for receipt and transmission of user messages; comprising the steps of on detection of a fault in the first communications link the at least one base station transceiver continues to transmit a beacon or pilot signal; followed by: monitoring mobile terminal activity in order to allow determination of whether the beacon or pilot signal is being transmitted from the at least one base station transceiver.
The present invention may also include a base station transceiver for a mobile telecommunications network for communication with mobile terminals, comprising: a monitoring system for monitoring the internal state of components of the base station transceiver handling traffic and/or control signals from or to the network which are to be transmitted to or received from the mobile terminals, respectively and for instructing a transmitter of the base station transceiver to continue transmitting beacon or pilot signals when it is determined that all internal components of base station transceiver are functioning correctly and the traffic and/or control signals from the network are defective, and for instructing the transmitter to stop transmitting the beacon or pilot signals if a fault is detected in one of the components of the base station transceiver and the traffic and/or control signals from the network are defective.
The present invention may also includes a method of operating a base station transceiver for a mobile telecommunications network for communication with mobile terminals, comprising the steps of monitoring the internal state of components of the base station transceiver handling traffic and/or control signals from or to the network which are to be transmitted to or received from the mobile terminals, respectively; and instructing a transmitter of the base station transceiver to continue transmitting beacon or pilot signals when it is determined that all internal components of base station transceiver are functioning correctly and the traffic and/or control signals from the network are defective; and instructing the transmitter to stop transmitting the beacon or pilot signals if a fault is detected in one of the components of the base station transceiver and the traffic and/or control signals from the network are defective.
The present invention may also include a network element for a mobile telecommunications network, the network element being in communication with at least a first and a second base station transceiver over a first and second data link, respectively, the first and second base station transceivers being in communication with a plurality of mobile terminals; the network element comprising: a first device for determining if the first data link to the first base station transceiver is defective, and a second device for providing activity data from mobile terminals received via the second base station transceiver and to allow a decision whether the fault is in the first base station transceiver or in the first data link. The second device may also be adapted to decide whether the fault is in the first base station transceiver or in the first data link.
The dependent claims define further individual embodiments of the present invention.
The present invention will now be described with reference to the following drawings.